Each day, as the sun’s rays pass through the hole in the analemma plate below the lintel of the south trilithon, the sun casts a spot surrounded by a shadow on either the horizontal or vertical face of the two stones north of the trilithon. Over the course of a year, the noon locations of these spots generate a figure 8, or analemma. The spots cast on the etched analemma provide two pieces of information: they indicate noon Central Standard Time, or 1 p.m. Daylight Saving Time, each day and show the day of the year. The spot reaches a high point on the analemma at the winter solstice on December 21 and a low point at the summer solstice on June 21. Because the configuration does not recognize the extra day of leap years, the analemma plate’s design includes provisions for adjustments to compensate for the difference between solar and calendar years.
